On April 18, an Indian Army brigadier led a small delegation of officials to meet his Chinese counterpart, a senior colonel, in Chushul in Ladakh . The flag meeting had been called for by the Indian Army. They wanted to know what a platoon-sized unit of 23 PLA (People's Liberation Army) troopers was doing nearly 10 km deep inside Indian territory. The Chinese patrol had pitched their tents and had been discovered the previous day by the Indo-Tibetan Border Police (ITBP). The Chinese response stunned the Indian side. They quoted a November 1959 letter of Chinese premier Chou En Lai to Jawaharlal Nehru to bolster their claim to the entire area. India was constructing bunkers in Chinese territory, the pla officials told the Indian Army delegation. The Chinese had come there merely to observe them. A second flag meeting called on April 23 failed to resolve the stand-off. The soldiers stayed put in their tents.

An Indian patrol near the line of actual control in Ladakh.Two decades after India and China agreed to maintain "peace and tranquillity" on the border, "transgressions" as India calls intrusions by China, have followed a familiar pattern: PLA soldiers intrude into the 4,000 km disputed border to mark their presence with cigarette packets, soup cans and slogans painted on rocks. India has recorded over 500 such incursions since 2010. But the April 17 stand-off has stunned the security establishment. "Not only have the Chinese done what they hadn't before but they seem determined to stay longer," says an intelligence official.

China's brazenness shocked India's military-diplomatic establishment in South Block. The visit of Chinese defence minister General Liang Guanglie in September 2012 heralded the revival of joint army exercises that had been put off after China's 2010 refusal to grant a visa to India's northern army commander. This month, China confirmed a May 20 visit by Premier Li Keqiang to New Delhi. In January, a senior foreign ministry official predicted 2013 would be the year of greater engagement with China. Recent peace overtures towards India even led a senior defence ministry official to conjecture that China was focused on its dispute with Japan and did not want to antagonise India.

Nothing could be further from the truth. Because just as eight Chinese coast guard patrol ships steamed into Japanese territorial waters around the disputed Senkaku islands in the East China Sea, Chinese helicopters were resupplying their soldiers nearly 10 km deep inside Ladakh. Even an April 19 demarche to the Chinese envoy Wei Wei by Foreign Secretary Ranjan Mathai for the "restoration of status quo on the border" failed embarrassingly. A Chinese foreign ministry spokesperson denied any transgression.

The incident rapidly shot up the chain from a tactical to a diplomatic and, finally, a political issue. Union Defence Minister A.K. Antony said in Delhi that India would "take every step to protect its interests". An identical number of the Army's Ladakh Scouts and itbp troopers pitched their tents barely 100 metres away from the Chinese troops. The Indian Army, which has advised restraint, has called for a meeting of the division commanders of both sides on a date yet to be decided. India hopes for an early resolution, though what would make the Chinese withdraw is not known. "If the Chinese are determined not to lose face then they will not leave without any reciprocal measures. Then it becomes a problem," says former foreign secretary Kanwal Sibal. "India does not have much of a choice except to stand its ground and discuss the issue at a diplomatic level."

"To safeguard Tibet and as part of competitive conflict, the LAC (Line of Actual Control) will be kept tense to exercise leverage and humiliate weaker India," tweeted former northern army commander Lt General H.S. Panag.

The 320 km LAC extends from Daulat Beg Oldi (DBO) in north-eastern Ladakh to Demchok in the south. In recent years, India has moved to assert control over the high-altitude desert. In 2008, the Indian Air Force reactivated a disused airfield in DBO at 16,200 ft located just 8 km away from the LAC. An-32 medium transport aircraft could now resupply posts in DBO manned by ITBP, Ladakh Scouts and the Army. It took nearly 10 days to reach the remote posts on muleback earlier. Last year, the Army completed a new 80-km road along the gorge of the Shyok river from Leh to DBO which could resupply the posts. "China must have realised Aksai Chin's vulnerability in case of a border war," says a senior Army officer.

Last month, China's new President Xi Jinping unveiled a five-point formula to improve ties with India. The formula included maintaining peace and tranquillity on the border. But incursions are hardly likely to speed up a resolution.